1. Field of the Invention
The present invention is directed to x-ray diagnostics installation, and in particular to such installations suitable for mammography exposures.
2. Description of the Prior Art
A knowledge of the amount of radiation to which a patient has been exposed in the production of an x-ray exposure is needed to estimate the radiation risk to the patient. In addition to being dependent upon known characteristics of a particular x-ray apparatus, the radiation exposure is dependent on data which may change from exposure to exposure, such as the tube voltage, the product of the tube current and the duration which the tube is energized by the automatic exposure unit, and the attenuation of any filter which may be used. The radiation exposure is also dependent upon the sensitivity of the imaging system (film-foil system) and on the thickness of the subject. The dose quantity relevant for estimating the radiation risk is the mean parenchyma dose. Given a known sensitivity of the imaging system, and an exit radiation dose defined as a result thereof, the mean parenchyma dose can be calculated by measuring the entry dose. It is not usually possible, however, to undertake a simultaneous measurement of the x-ray dose with the production of an x-ray exposure of a patient. It is known, however, to calibrate an x-ray installation using a phantom, which is equivalent to the tissue to be examined, so that an estimate of the mean parenchyma dose can be undertaken by measuring the product of the tube current and the duration of the exposure time.